European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society
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Progression of superior adjacent segment degeneration (PASD) could possibly be avoided by dynamic stabilization of an initially degenerated adjacent segment (AS). The current study evaluates ex vivo the biomechanics of a circumferential fixation connected to posterior dynamic stabilization at the AS. 6 human cadaver spines (L2-S1) were stabilized stepwise through the following conditions for comparison: intact spine (ISP), single-level fixation L5-S1 (SLF), SLF + dynamic AS fixation L4-L5 (DFT), and two-level fixation L4-S1 (TLF). For each condition, the moments required to reach the range of motion (ROM) of the intact whole spine segment under ±10 Nm (WSP10) were compared for all major planes of motion within L2-S1. ⋯ The moments required to reach WSP10 increase dependent on the number of fixated levels and the fixation stiffness of the implants used. Additional fixation shifts motion to the superior segment, according to fixation stiffness. Therefore, dynamic instrumentation cannot be recommended if prevention of hyper-mobility in the adjacent levels is the main target.
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Linezolid belongs to a new class of synthetic antimicrobial agent that is effective for a variety of methicillin-resistant Staphylococcus aureus (MRSA) infections including bone and joint MRSA infections, but the effectiveness of linezolid for the treatment of MRSA spine infection remains controversial. In this study, we investigated the diffusion of linezolid or vancomycin into normal rabbit spinal tissues to determine the adequacy of linezolid for the treatment of spinal infection. ⋯ The penetration efficacy of linezolid into the bone marrow and iliopsoas muscle (88 and 84%, respectively), however, was higher than that of vancomycin (67 and 9%, respectively). These results suggest that linezolid is inadequate for the treatment of spine infection limited to the intervertebral disc, but may be effective for the treatment of infection extending into the muscle and bone marrow, such as in vertebral osteomyelitis, iliopsoas abscess, and postsurgical infection.
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Degenerative lumbar spinal stenosis is the most common reason for lumbar surgery in patients in the age of 65 years and older. The standard surgical management is decompression of the spinal canal by laminectomy and partial facetectomy. The effect of this procedure on the shear strength of the spine has not yet been investigated in vitro. ⋯ The median shear stiffness was 197.4 N/mm (range 119.2-216.7) with laminectomy and partial facetectomy which was significantly (p = 0.036) smaller than the stiffness of the control specimens (median 216.5, 188.1-250.2). It was concluded that laminectomy and partial facetectomy resulted in 22% reduction in ultimate shear force to failure and 9% reduction in shear stiffness. Although relatively small, these effects may explain why patients have an increased risk of sustaining shear force related vertebral fractures after spinal decompression surgery.
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Transpedicular fixation can be challenging in the osteoporotic spine as reduced bone mineral density compromises the mechanical stability of the pedicle screw. Here, we sought to investigate the biomechanical and histological properties of stabilization of expandable pedicle screw (EPS) in the osteoporotic spine in sheep. EPSs and standard pedicle screws, SINO screws, were inserted on the vertebral bodies in four female ovariectomized sheep. ⋯ Histologically, newly formed bone tissues grew into the center of EPS and were in close contact with the EPS. Our results show that the EPS demonstrates improved biomechanical and histological properties over the standard screw in the osteoporotic spine. The EPS may be of value in treating patients with osteoporosis and warrants further clinical studies.